In cold climates, particularly where occupied spaces must be heated, air in these spaces tends to have low relative humidity. This is uncomfortable, encourages static electricity discharges and is sometimes even unhealthy. Humidifiers are routinely used in heating, ventilation and air conditioning (HVAC) systems to add moisture to the air being conditioned to enhance the comfort of the occupants of the conditioned air space. The current relative humidity and the temperature of the air being conditioned dictate the amount of moisture added.
Humidifiers have a variety of different designs. There are small stand-alone units intended for a single room. Larger units are designed for permanent installation as a component of a central heating/HVAC system. These add moisture to the stream of heated air passing through the furnace duct to the conditioned space. The latter type of humidifier will hereafter be referred to as an “in-duct” humidifier. The humidifier whose description follows is an improvement to one common type of in-duct humidifier.
There are a number of different designs for in-duct humidifiers. The kind which is presently of interest has an air-permeable pad, typically made from a number of similarly-sized layers of thin, expanded aluminum sheet stacked to a thickness of perhaps 1.5 in. The layers of aluminum sheet are bonded to each other so as to create a pad structure having a rectangular box-like shape. The pad is placed in or near the furnace duct so that air warmed by the furnace can flow through the pad. Water is caused to drip onto the top surface of the pad at a rate which keeps the pad moist from top to bottom when humidity is demanded. The warm air passing through the pad evaporates water in the pad, adding humidity to the air and thereby raising the relative humidity.
The water flows onto the pad from what is known as a water distribution tray, or simply a tray. The tray extends along the top surface of the pad and has a reservoir for directing water flow over the pad. Water is fed to the tray from the building water supply and flow is controlled by a solenoid valve. Apertures spaced along the tray bottom permit the water flowing into the tray to fall onto the top of the pad. By properly selecting the rate at which water is added to the tray, the pad can be kept moist from top to bottom. The pad, the tray, and a frame supporting the pad and tray in the proper spatial relationship comprise the most important elements of an in-duct humidifier. It is very important, for efficient operation, that the tray evenly distributes water across the entire width of the pad.
There are water distribution trays now known which have a number of apertures spaced apart along the length of the tray and that use individual ducts, or channels, for conducting water to each aperture. Ideally, sizing and positioning the individual channels to conduct water to the apertures allows each aperture to receive an equal measure of the water; thereby assuring that the pad is evenly soaked across its width in accordance with the water demanded. These designs do not always fully realize these goals and indeed may sometimes cause further problems. For example, problems may arise that still prevent uniform saturation of the pad. This may happen if the tray is not perfectly level, thereby preventing an equal amount of water from flowing to each part of the pad's top surface. This is a fairly common problem as there is generally little need to accurately level other elements of the heating/HVAC system. Thus, when the humidifier is installed, it will usually be only as level as the air duct at that location. Water distribution will then likely favor one end of the tray over the other end.
It is also very important for all of the water in the tray to promptly drain onto the pad when the water flow stops. This eliminates un-drained pools of water standing in the tray which will evaporate leaving behind minerals, originally dissolved in the water, pooled on the tray surfaces. Over time, these mineral deposits can build up to a level which interferes with the operation of the tray itself. The use of a number of individual channels to supply water to individual holes tends to exacerbate this problem.
Accordingly, what is needed in the art is a water distribution tray that does not suffer the limitations of the prior art.